[SR-5012] "warning: pointer not aligned at address" when using keypaths

[aciidgh]

Previous ID	SR-5012
Radar	rdar://problem/32318829
Original Reporter	@aciidb0mb3r
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 7d678c6e72864c0bbfd6450252c0b0de

Issue Description:

struct Version {
    let _version: Int
}

extension Int {
    var isEmpty: Bool {
        return false
    }
}

let kp = \Version._version.isEmpty

$ swiftc x.swift
ld: warning: pointer not aligned at address 0x100004644 (l_keypath + 60 from /var/folders/98/0fcj8gms75z3x7_01g5v_m0h0000gn/T/x-295e1d.o)
ld: warning: pointer not aligned at address 0x10000463C (l_keypath + 52 from /var/folders/98/0fcj8gms75z3x7_01g5v_m0h0000gn/T/x-295e1d.o)

[belkadan]

I saw a warning like this too, but didn't realize it was related to key paths. @jckarter, any ideas?

[belkadan]

@swift-ci create

[jckarter]

Key paths use a packed layout to save memory, since we only really need 12 bytes per component in the common case and pointer alignment would make components take 1/3 more space, but this causes problems for dyld in statically-emitted literals. We're tracking this internally as rdar://problem/32318829.

[tkrajacic]

I just ran into this in Xcode 9 beta and created a stripped down example, but I guess you are all set here? (That'll teach me to search for bugs here before creating example projects... 😉 )

[jckarter]

Thanks @tkrajacic! I already know what the problem is, but I appreciate you narrowing it down.

[jckarter]

PR for master: #10419
PR for 4.0: #10420